(1) Field of the Invention
The present invention relates to sealant compositions and methods for encapsulating friable materials used for thermal insulation, fireproofing, acoustical insulation and decorative finishes and is particularly applicable to the treatment of asbestos-containing materials.
(2) Description of the Prior Art
In recent years there has been an increasing awareness of the importance of environmental factors in carcinogenesis. The recognition of widespread environmental contamination by asbestos-containing materials has been of particular concern.
Such concern is evidenced in approximately twenty Federal regulations under various laws which regulate human an environmental exposure to asbestos. Despite these regulations, large segments of the population continue to be exposed to this dangerous material especially material in friable form.
The extensive use of asbestos in commerce and industry has created a health hazard of serious consequences for persons inhaling or ingesting the substance. Since the beginning of the century, asbestos has been used as a major constituent or an important additive to many consumer products so that there are many sources of exposure to the general public. For almost forty years asbestos has been widely used in building construction having been sprayed or applied onto structural steel to retard structural collapse during fire and to ceilings and walls for purposes of acoustic and thermal insulation, decoration and condensation control. Many insulation materials consist of a mixture of asbestos and mineral-, rock-, slag-wool or fibrous glass. In other formulations wood pulp and paper fibers are non-fibrous binders such as plaster of Paris, vermiculite, perlite and clay are used. Asbestos has also been used extensively as decorative and textured-spray finishes or paints. The asbestos content of these materials is usually found in the range of 5 to 50 weight percent. Some of this asbestos containing material is now known to be damaged or deteriorating and releasing fibers into the building environment.
Unlike most chemical carcinogens asbestos mineral fibers persist in the environment almost indefinitely and represent a continuous source of exposure. Asbestos fibers cannot be easily destroyed or degraded. The size and shape of these fibers give them aerodynamic capability to permit them to remain suspended in air for many hours. The fibers can become suspended in the air and are then available for respiration and retention in the lung. Fibers which have settled to the floor can be reentrained by the slightest activity in the area. Thus, even though the release of fibers may be intermittent, there is a potential for continuous exposure.
Friable material is material that can be crumbled, pulverized or reduced to powder under hand pressure. Friable material may be an asbestos-containing material or it may be a material that contains other fibers such as cellulose and glass fibers. Friable asbestos material draws particular attention since it is likely to release fibers with minimum disturbance of the surface, cause serious contamination and exposure problems and it has been used in many buildings having high population densities including schools, office buildings and high-rise apartment buildings. Furthermore, as friable asbestos material ages, it can lose its cohesive strength and more readily releases fibers. These materials were usually applied by spraying but have also been applied by troweling and brushing. They are friable in varying degrees depending on the components of the material, the amount of cement or binder added, and the method of application. Sprayed material is usually soft. Cementitious material varies from soft to relatively hard. Several methods have been proposed to eliminate or substantially reduce exposure of friable asbestos material such as by removal, encapsulation and enclosure. For encapsulation, the asbestos material is coated with a sealant. The sealing of sprayed asbestos surfaces involves applying material that will penetrate and envelop the fiber matrix and coat the surface portions to eliminate fallout and protect against abrasion damage as well as physical damage due to impact.
Sealants for friable materials which are currently available include water-based latex polymers, water soluble epoxy resins and organic solvent-based polymers of various types. However, none of these sealants have been commercially successful because they fail to provide one or more of the desirable properties required. Shortcomings associated with the available sealant compositions include the need for high-pressure application, lack of penetration, poor flexibility of the encapsulated asbestos-containing material, unacceptable impact strength and abrasion resistance, poor adhesive and cohesive strength. Also several sealant compositions have been found unacceptable since they are combustible and during combustion they generate smoke and release toxic gases.
Therefore, a need persists for a sealant composition for friable material which avoids all of the drawbacks of the prior art compositions.